Essentially all types of rubber, both natural and synthetic, and particularly rubbers formed from conjugated dienes, are known to be susceptible to deterioration resulting from prolonged exposure to oxidative aging.
Improved aging stability of polymers is of high interest. Particularly important are non-extractable antioxidants which are desirable for food contact end uses. Elastomers and resinous materials having low volatiles are required in many end uses, yet non-bound antioxidants are volatile.
Much effort has been expended in the field of polymer technology to develop various stabilizers that will inhibit effectively the adverse effects of aging of polymeric compositions.
Antioxidants for the most part are mixed with or compounded with various polymers. However, such admixed stabilizers frequently are lost in further compounding, utilization, admixing, blending, and the like, or leached out in use of the polymer, or even volatilized when the polymeric products are exposed to elevated temperatures over prolonged periods of time.
Efforts to bind the antioxidant to the polymer have been employed in the past, but have used or required large amounts of reactive antioxidant. U.S. Pat. No. 4,138,389 prepares a low molecular weight polymer containing a multiplicity of functional groups which are reactable with certain stabilizers to form a material then dilutable with untreated polymer.
U.S. Pat. No. 4,098,709 uses a carboxylic acid group-containing polymer which is reacted with a hindered phenol in order to put the protective entity along the chain wherever the carboxylic acid group may be found. U.S. Pat. No. 4,107,144 copolymerizes a dialkylphenol antioxidant with a vinylic group containing monomer by means of a Friedel-Crafts catalyst to produce thereby a bound antioxidant-containing polymer. U.S. Pat. No. 3,658,769 copolymerizes certain nitrogen-containing compounds with one or more comonomers in order to try to achieve an antioxidant-property exhibiting polymer.
Needed, still, are improved methods of introducing antioxidant functions by chemical methods.